Quantum mechanics is the physical description of how atoms behave. Unlike classical Newtonian physics, it involves instantaneous transitions, set by probabilistic rules rather than exact, mechanistic laws. Einstein objected to the jumpiness, chance elements and other indeterminate aspects of quantum theory, whereas Bohr found these acceptable. As Wheeler came of age as a physicist in the mid-to-late 1930s, he became close friends with both debaters, appreciated their well-reasoned arguments, and hoped to find a way of reconciling their clashing viewpoints.